1. Field of the Invention
The present invention relates to semiconductor devices using substrates having flexibility.
2. Description of the Related Art
A substrate having flexibility has advantages in that mechanical strength with respect to vibration and shock is excellent as compared to a glass substrate, the thickness is easily suppressed, and a degree of freedom in shape is high. Therefore, a semiconductor device using the substrate having flexibility is expected to have various applications. The substrates having flexibility may include a substrate which does not have heat resistance high enough to withstand heat treatment in a manufacturing process of a semiconductor element. For this case, a manufacturing method is proposed in which after a semiconductor element is formed over a substrate having heat resistance which is separately prepared, the semiconductor element is separated from the substrate to be bonded to the substrate having flexibility.
The present applicant proposes techniques of separation and transfer, which are described in Reference 1 (Japanese Patent No. 3364081) and Reference 2 (Japanese Patent No. 3406727). In Reference 1, a technique is described in which separation is performed by removing a silicon oxide layer which serves as a separation layer by wet etching. In Reference 2, a technique is described in which separation is performed by removing a silicon layer which serves as a separation layer by dry etching. Further, the present applicant proposes techniques of separation and transfer, which is described in Reference 3 (Japanese Published Patent Application No. 2003-174153). In Reference 3, a technique is described in which, in forming a metal layer (Ti, Al, Ta, W, Mo, Cu, Cr, Nd, Fe, Ni, Co, Ru, Rh, Pd, Os, or Ir) over a substrate and stacking an oxide layer thereover, a metal oxide layer of the metal layer is formed at the interface between the metal layer and the oxide layer, and the metal oxide layer is utilized for separation in a subsequent step.